Dan Bostrom, the longest-serving member of the St. Paul City Council, will retire at the end of December, opening a seat that hasn't been vacant in more than 20 years.

Bostrom unexpectedly announced his retirement at the end of the council meeting Wednesday, reading a short statement during the time when council members typically share news from their wards.

"It's with a great sense of peace that I announce my retirement from the St. Paul City Council effective 31 December, 2018," Bostrom said. "I want to thank the various mayors and many colleagues that I had the pleasure to serve with on the council over the past 23 years, and I want to especially express my gratitude to the good people of Ward 6, who entrusted me to act as their representative on the council. It's been my deepest honor to have earned your respect and trust."

Once Bostrom had finished speaking, his fellow council members rose to their feet to applaud him. Council President Amy Brendmoen promised that the council will honor Bostrom at its final meeting of the year, scheduled for Dec. 19.

"You've had a wonderful run of service here and I think that there's a lot of people who would like to acknowledge the work that you've done here," she said, adding, "I'm shocked."

Bostrom, 78, grew up on the East Side of St. Paul at a time when the city still had streetcars. He joined the council in 1996 after a nearly 30-year career as a St. Paul police officer and nearly 10 years on the St. Paul school board. As a council member, he's pushed for economic development on the East Side, including the Phalen Boulevard corridor.

As the council has skewed left since he joined it, Bostrom has remained a moderately conservative voice and has at times offered up the lone dissenting vote. In November, he was the only council member to vote against a resolution that nixed putting organized trash collection on the ballot. And before announcing his retirement Wednesday, he was the lone vote against adding support for marijuana legalization to the council's 2019 legislative agenda.

Still, Bostrom has collaborated with other council members even when they disagree on issues, said former Council Member Dave Thune.

"I'm a lefty knee-jerk liberal and Dan is a moderate, but we're best friends," Thune said. As a council member, "he really believed in people and he liked representing regular folks and speaking common sense."

In an interview Thursday, Bostrom said he decided to retire before the end of his council term in part because he "was not interested in serving out a term as a lame duck."

An interim council member will fill Bostrom's seat until Dec. 31, 2019. The council must choose that person within 30 days after Bostrom's last day.

This is the second departure from the seven-member council this year — in January, Council Member Russ Stark left for a job in Mayor Melvin Carter's office.

The entire council will be up for re-election in November, with new terms starting in January 2020.